Low-tech
Graywater Systems
Let gravity do the work.
The simplest distribution systems are landscape direct, meaning they have no storage and no filtration and passively flow directly into the landscape as the graywater is being produced.
Laundry-to-Landscape
system redirects graywater from the discharge hose of your washing machine through an irrigation line with outlets to mulch basins close to specific plants.
Doesn’t alter existing plumbing
No permit required (if guidelines are followed)
Easy to install
Low cost
Washing machine pump provides some pressure which provides more tolerance to variations in the slope
Uses 1” PVC and/or Polyethylene pipe.
Branched drain
(showers, sinks, laundry or whole house).
A gravity fed passive system that diverts graywater into the landscape through a branching network of distribution pipes.
Uses mulch basin irrigation
Uses “flow splitter” fittings to divide flow among several outlets
Typically requires a permit due to necessary alterations to existing plumbing
Uses 1.5”-2” ABS or PVC-DWV pipe
Constructed Wetlands
Wetland plants transpire large amounts of water (10+ gallons /day on warm days),so usually Constructed Wetlands are appropriate where there is excessive graywater and little irrigation demand or soilspace to use other infiltration system. Wetland plants remove nutrients and can help filter pollution out of wastwater and are used in large scale wastewater treatment plants as well. Gravel and other aggregate beds can ultimately suffer clogging problems/overflowing of graywater requiring replacement or flushing.
Photo creditL: Greywater Action
Common features of low-tech systems
3-way diverter valve
Different systems use different size valves (laundry-to-landscape= 1” valve, branched drain = 2”-3” valve) but the concept of controlling the diversion is always the same. The 3-way valve allows the user to redirect flow back to the sewer or septic in case you have to wash something toxic or hazardous (ie. automotive grease, paint brushes, chemicals from home photo lab, diaper water etc.), or if seasonal weather conditions such as high groundwater or precipitation levels makes it difficult to infiltrate graywater without causing runoff (which is prohibited). The 3-way valve must be labeled and “easily accessible”. Often for branched drain systems the valve is located in a crawlspace, and is connected to a remote controlled motor called an “actuator” that allows the user to operate it from a switch located conveniently in the house.
Mulch Basin Irrigation
To avoid the notorious clogging typical with unfiltered graywater, low tech systems use relatively large drain pipes (1.5”-2” diameter) and shielded outlets designed to be highly resistant to clogging. The outlets release graywater into a mulch basin, created by excavating out the soil and refilling with wood chips, gravel drain rock, or other chunky organic material providing open pore space in which the surge of graywater fills preventing it from being exposed to the surface (which is prohibited). The size of the mulch basins are determined by simple calculations based on the soil type, numbers of gallons produced per day, and the anticipated maximal surge volume anticipated.
Passive flow division
To be able to divide the flow of graywater among multiple outlets, low-tech systems branch apart using a passive system of division. The branched drain system uses a special fitting called a “double ell” which splits the flow approximately in half (if the flow splitter is level), and the laundry-to-landscape system uses “Tee” fittings that tap off a larger main supply line to sends fractions of the total flow to different outlets.
